The surviving suspect in the Boston Marathon bombing was moved today to a prison hospital outside Boston. Officials say Dzhokhar Tsarnaev is no longer cooperating with investigators. Some members of Congress, meanwhile, say the FBI should have heeded Russian warnings that Dzhokhar's elder brother had become a follower of radical Islam.

As NPR's Tom Gjelten reports, the failure to connect dots in a terrorism case is a criticism we've heard before.

TOM GJELTEN, BYLINE: In hindsight, the dots seem to be there: Tamerlan Tsarnaev grows increasingly alienated from his American life. He turns to Islam and shows interest in extremist movements in Dagestan, where his parents live. Russian intelligence twice alert U.S. authorities to their concerns about him. In response, the FBI interviews Tsarnaev but finds nothing notable. Later, he goes to Dagestan for six months.

On his return, however, the FBI does not re-interview him. That's what bothers the bureau's critics. Here's Republican Congressman Ted Poe of Texas speaking at a House hearing today.

(SOUNDBITE OF CONGRESSIONAL HEARING)

REPRESENTATIVE TED POE: They tell us two times that this is somebody that we ought to be concerned about. Wouldn't you think, in the area of intelligence, that'll raise a red flag?

GJELTEN: Easy for him to say. Andy Liepman, a veteran CIA officer and former deputy director of the National Counterterrorism Center, says U.S. authorities move carefully in investigating Americans. In the case of a tip about an ethnic Chechen living legally in the United States, they would first consider the source.

ANDREW LIEPMAN: Before this event, if someone had come to you and said, you know, the Russians have told us that this American, a legal permanent resident, Chechen nationality, has radical Islamic connections, we want you to do something about it. You know, the first thing that would have popped into your head was: The Russians are up to something.

GJELTEN: After all, the Russians for years have been on the lookout for Chechen separatists. What action counterterrorism officials will take in response to a tip about someone, Liepman says, depends on what that person has been alleged to do.

LIEPMAN: It's one thing to think radical thoughts. It's quite another to take that, mobilize and take violent action.

GJELTEN: The importance of distinguishing between thinking and acting is due, in part, to First Amendment rights. Philip Mudd, who worked for more than 25 years at the CIA and also at the FBI, notes law enforcement can't do anything about someone who says he hates the USA, or hates President Obama, or hates some federal judge.

PHILIP MUDD: Hatred is not a federal violation. Saying, you know, I think we ought to drive by the judge's house and take a look, then I'm going to say, game on. That suggests to me that you're considering taking an action against a federal officer.

GJELTEN: Looking at extremist websites is not illegal. Law enforcement officials are also limited by the resources and manpower they have available to carry out investigations. U.S. officials, defending what they did in response to the Russian tips about Tamerlan Tsarnaev, point out that there are hundreds, perhaps thousands, of individuals about whom they receive tips.

Philip Mudd, who, after his CIA service, directed the National Security Department at the FBI, knows that if someone had enough suspicious behaviors to distinguish them, it would be different.

MUDD: If he were the only guy in the lens, that's pretty interesting. But you've got to look at this in the context of the thousands and tens of thousands of investigations that go on in this country, many among people who look a lot uglier than this guy.

GJELTEN: This guy being Tamerlan Tsarnaev. The relevant comparisons here are to the cases of Nidal Hasan, the Army major who went on a shooting rampage at Fort Hood, Texas, and Umar Abdulmutallab, who tried to blow up a civilian airliner over Detroit. Counterterrorism officials later acknowledged they had missed important signs about those two. But so far, at least, evidence that clues were missed in this case have not been found.